In motor racing grid is a term which can mean either the group of cars competing in a race and or the area just behind the start/finish line where the cars are positioned, using markings painted on the track surface, ready for the start. Grid position is often dictated by performance in qualifying, with the fastest driver/car combination taking pole position. In some race series other factors such as performance in previous races is used to determine the grid positions.
Outside motor racing, grid refers to the mains electricity supply network, which in the UK is called the National Grid. So 'grid electricity' means electricity from mains supply, rather than electricity from a vehicle's on-board battery.